EFFECT OF VACUUM ANNEALING ON OXYGEN STOICHIOMETRY AND RESISTIVITY OFSOL-GEL DERIVED LA0.7SR0.3MNO3-DELTA FILMS

We have studied the dependence of the resistivity and magnetoresistanc e (MR) of epitaxial (0 0 1) La0.7Sr0.3MnO3-delta/(0 0 1) LaAlO3 firms on controlled vacuum annealing. First, La0.7Sr0.3MnO3-delta films grow n by sol-gel process were annealed at O-2 (1 atm. oxygen)/1170 K/1 h ( we call this as-prepared films); subsequently, these as-prepared films were annealed in vacuum (similar to 10(-6) torr/2 h) at different tem peratures, i.e. 720 K, 770 K, 820 K, 920 K, to systematically reduce t he oxygen stoichiometry. The resistivity increases systematically with increasing annealing temperature in accord with oxygen content variat ion. The resistivity shows a metallic behavior (as-prepared films), me tal-insulator transitions (films annealed at 720 K, 770 K) and an insu lating behavior (firms annealed at 820 K, 920 K). Significant MR is ob served predominantly near the resistivity peak for the metallic films and at low temperature for the insulating films. These observations de monstrate that the oxygen content, the resistivity and MR behavior of manganese oxides are precisely controllable via vacuum annealing. (C) 1997 Published by Elsevier Science Ltd.